https://www.uscis.gov/citizenship/find-study-materials-and-resources/study-for-the-test
Anything related to your immigration history, marital status.
This depends on whether you have I-751 pending. If you do, make sure to bring your spouse and updated marital evidence. Tax returns are useful to have to prove good moral character. If you had any criminal convictions - documentatiob around that. Any marriages / divorces, kids info. I'd bring those.